Seismic instrumentation plan for the Hawaiian Volcano Observatory

Abstract

The seismic network operated by the U.S. Geological Survey’s Hawaiian Volcano Observatory (HVO) is the main source of authoritative data for reporting earthquakes in the State of Hawaii, including those that occur on the State’s six active volcanoes (Kīlauea, Mauna Loa, Hualālai, Mauna Kea, Haleakalā, Lō‘ihi). Of these volcanoes, Kīlauea and Mauna Loa are considered “very high threat” in a report on the rationale for a National Volcanic Early Warning System (NVEWS) (Ewert and others, 2005). This seismic instrumentation plan assesses the current state of HVO’s seismic network with respect to the State’s active volcanoes and calculates the number of stations that are needed to upgrade the current network to provide a seismic early warning capability for forecasting volcanic activity. Further, the report provides proposed priorities for upgrading the seismic network and a cost assessment for both the installation costs and maintenance costs of the improved network that are required to fully realize the potential of the early warning system. HVO has operated seismometers on the Island of Hawai‘i since 1912. Currently, the seismic network includes more than 70 stations from four different organizations. Generally, the Island of Hawai‘i has most of the seismic stations in the network (and most of the activity), with the density of seismic stations increasing from the northern part of the island to the south-southeast. The strength of the current network, based on theoretical detection and location capabilities, is at the summit of Kīlauea Volcano and Kīlauea’s upper East Rift Zone and Pu‘u ‘Ō‘ō—where few, if any, upgrades need to be made to the seismic network. The network in the region between Kīlauea and Mauna Loa is slightly weaker, as is the summit of Mauna Loa. In general, the rift zones of each volcano are more poorly monitored seismically than the summits and thus require a greater number of stations to achieve a volcanic early warning capability for monitoring seismicity. Priorities for new seismic installations on the volcanoes depend on several factors, including current activity, historical activity, population exposure, and current network quality. On Kīlauea, new installations on the middle East Rift Zone, lower East Rift Zone, and lower Southwest Rift Zone appear to be the highest priorities. On Mauna Loa, improvements to the summit seismic network should be prioritized based on the analysis of the data, followed by the installation of a sparse network on both rift zones. Once installed, the next priority would be to create denser seismic networks on the rift zones, particularly where eruptions could quickly threaten populated areas (middle Northeast Rift Zone, lower Southwest Rift Zone). On Hualālai, analysis of the data indicates that the Northwest Rift Zone is the most important priority, particularly where it runs through the population center of Kalaoa. Hualālai’s South Rift Zone appears to be the lowest priority for additional seismic instrumentation of any rift zone on Kīlauea, Mauna Loa, or Hualālai because of its low historical activity and lack of population exposure. Mauna Kea and Haleakalā have less active historical eruptive activity and thus have more modest proposed upgrades to seismic instrumentation. The installation of new seismic stations is only the first part of building a volcanic early warning capability for seismicity in the State of Hawaii. Additional personnel will likely be required to study the volcanic processes at work under each volcano, analyze the current seismic activity at a level sufficient for early warning, build new tools for monitoring, maintain seismic computing resources, and maintain the new seismic stations.